1. Field of the Invention
The present invention relates to semiconductor devices, and more particularly, to a method of sputtering tungsten diffusion barriers in contact and via holes in semiconductor devices having increased robustness.
2. Description of Related Art
In the manufacture of semiconductor devices, metal conductive layers are patterned for the purpose of making interconnections between different points on the device. After formation of this patterned metal conductive layer, an electrically insulative material such as silicon dioxide or silicon nitride is deposited over the metal conductive layer by conventional deposition techniques. The surface of this electrically insulative layer will routinely be uneven due to the uneven underlying contour of the patterned conductive layer. The presence of a metal interconnect path beneath the insulative layer results in a corresponding elevated path in the surface contour of the insulative layer.
Often it is necessary, especially in high density devices, to form additional patterned conductive layers on the surface of the insulative layer. In order to interconnect the metal conductive layers to each other and to the substrate, the generally followed practice is to etch holes in the insulative layer prior to deposition of a metallic layer onto the insulative layer. These holes or "vias" are located in positions where contacts are desired between conductive regions, such as previously deposited patterned metal layers, or conductive substrate layers underlying the insulative layer and metal patterns deposited on the insulative layer. Vias are best visualized as cylinders which are filled with a metal so that devices located on different metallization levels can be electrically connected.
Vias are typically formed by applying a resist mask to the insulative layer. The resist mask is patterned and etched to form openings where via holes are to be etched into the insulative layer. An etchant is then applied to the mask layer such that via holes are etched where openings occur in the etching mask. The etching mask is then removed from the surface of the insulative layer and a metal layer is deposited on the insulative layer.
Prior to deposition of the metal layer the via may be filled with another metal to form a via stud. Such techniques as chemical vapor deposition of tungsten (CVD-W) followed by planarization of the blanket tungsten film may be used to form a tungsten via stud. However, during CVD-W to fill the via, the underlying materials are often attacked by the chemicals used in the CVD process. This requires a robust diffusion barrier to be deposited into the via between the underlying metal, usually aluminum, and the CVD-W chemistry, and to act as an adhesion layer for the CVD-W. Robustness is considered in the industry as encompassing the reliability, quality, and low failure rate of the diffusion barrier. Robustness of the diffusion barrier is important since failure of the barrier films result in attack of the underlying structures and/or defects in the CVD-W stud. Despite significant improvements in the barrier film quality, failure of these barriers is still a serious problem in semiconductor manufacture.
The prior art is replete with the use of diffusion barriers comprising titanium adhesion films alone or with titanium nitride or tungsten films. These films are generally deposited by physical vapor deposition (PVD), also known as sputtering, with the use of a collimator. Sputtering techniques using collimators, or collimation, traditionally give excellent step coverage in high aspect ratio vias by focusing the spray of the sputtered material. However, it has been found that during collimation tremendous energy is created which is transferred to the silicon wafer of the semiconductor device. Temperatures exceeding 420.degree. C. are possible leading to extrusion of the aluminum lines. It is desirable to have a process of depositing diffusion barrier films which does not employ such high temperature or result in aluminum extrusion but still provides robust barrier films and achieves the needed step coverage required in high aspect ratio vias.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of sputter depositing a tungsten diffusion barrier film without employing excessively high temperatures.
It is another object of the present invention to provide a method of depositing a tungsten diffusion barrier having improved robustness.
It is a further object of the present invention to provide a method of depositing a tungsten diffusion barrier film which does not result in aluminum line extrusion.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.